A COMPARISON OF SURFACE PREPARATION FOR COATINGS BY

WATER JETTING AND ABRASIVE BLASTING

Lydia M. Frenzel, Ph. D.Advisory Council

San Marcos, Texas, U.S.A.Prepared and Presented at 1999 WJTA Conference; Houston TX. Printed in the Proceedings.

ABSTRACT

Water Jetting, with and without abrasive addition, continues to impact the maintenance industry and displace some of the traditional areas of dry abrasive blasting. This presentation focuses on the similarities and differences in the visual reference photographs which are used in the global industry.

1. INTRODUCTION AND BACKGROUND

Since 1985, the continued improvement in nozzles, seals, and pumps make it possible for reliable removal of coatings and rust. Water jetting and wet abrasive blasting methods have gone from a rare oddity to acceptance by the marine industry and becoming the preferred process for removal of lead based paint or asbestos. The Technology Publishing Company's (TPC) annual survey of painting contractors indicates that fifty percent (50%) of the identified painting contractors use some type of high pressure or ultra-high pressure waterjetting or wet abrasive process. One individual contracting firm says they have cleaned over 20 million square feet of surface. Coatings manufacturers, notably International Paint Co. (Akzo Nobel), Hempel's Paints, and Jotun have produced videos, technical product literature, and visual reference photographs to train their technical representatives and clients. Ameron, Bridge-Cote of Canada, Devoe, Euro-Navy, Sigma, W&J Leigh & Co., Watson Coatings, and Wasser Hi-Tech Coatings are additional coating manufacturing companies who actively embrace the use of water in surface preparation.

Organizations such as SSPC ( Society for Protective Coatings), NACE Int. ( National Association of Corrosion Engineers), and ISO ( International Standards Organization) provide the grounds for consensus documents, that is, documents which are defined as a “general agreement” or a “majority of opinion.” Consensus recommended practices and technology updates provide a Common Language to describe problems. Every industry tends to define the same problems in different terms. Adopting consensus language saves time and money. Environmental concerns are driving movement to include water. Water Jetting and Wet Abrasive Blast Cleaning are displacing traditional abrasive blasting in certain areas. Adversarial points of views exist within the coatings industry. It took ten years to build a consensus and issue the first standard on the use of high pressure waterjetting jointly by NACE and SSPC in 1995.3 NACE and SSPC have issued two other documents since that time.2,11 In 1998, ISO also

started work on a separate water jetting standard as they did not know the extent of the American activities.

Over the years, European and American philosophies drifted apart in the adoption of consensus language for abrasive blasted cleaned steel. In simplistic terms, the Americans use standards language allowing a percentage coverage of stains, while the Europeans use a criteria of tightly adherent material. The visual reference photographs for abrasive blast cleaning showed examples of rusted steel, but not removal of coatings. Projects involving removal of coatings for repainting often call for leaving sound, adherent coatings on the substrate, not removing all of it to leave slight stains. These pictures don't exist as consensus photographs. The development of photos for high pressure water jetting is bringing the European and American working philosophies together as we consider the maintenance practices on a global basis.

In the fall of 1998, Dr. Frenzel drafted a letter which was sent to ISO over Ken Tator's, as the designated U.S. country expert to ISO TC 35 SC 12, signature with full support of SSPC and NACE organizations. " Dr. Lydia Frenzel, chair of the NACE and SSPC Joint Task Groups on water jetting and wet abrasive blast cleaning (TG D and TG I), and I would like to establish communication on a regular basis between the ISO working groups on surface preparation concerning water jetting and the Joint Task Groups in a mutually beneficial manner. Dr. Frenzel and I meet on a regular basis. We are concerned that the ISO groups may not fully aware of standards activities in the North America and wish to avoid conflict between working groups. We hope there will be commonality in standards development between the North American and the European communities. .........

We recognize that an independent set of photographs should be prepared so that coatings manufacturers do not have to refer customers to material originally prepared by a competitor. The U.S. National Shipbuilding Research Program funded the preparation of a set of photographs of surfaces prepared by water jetting specifically for standards preparation. These new photographs have been released to SSPC and NACE for preparation of visual reference photographs. ........

.....[we] hope that we can work together and provide a commonality to the water jetting and wet abrasive efforts."

Following this letter, ISO had a representative to the SSPC/NACE Task Group meeting in November, 1998, and members of the NACE/SSPC Task Group and the SSPC Executive Director, Dr. Bernard Appleman, met informally with ISO Working Group 2 on Water Jetting in March, 1999. Documents and working photos were exchanged. We opened communications and are currently working on development of new visual reference photographs for the Water Jetting of substrates, in particular steel, with the Europeans. This is vitally necessary as coatings suppliers and contractors work globally.

The majority of the slides used in this presentation are proprietary to individual companies or are actual slides of the draft photos under consideration by the standards groups. As such, they are not reproduced in this paper.

2. DEFINITIONS USED BY COATINGS INDUSTRY

The paper will be using definitions from SSPC and NACE technical reports and standards which are closely aligned with the WJTA Recommended Practices for the Use of Manually Operated High Pressure Water Jetting Equipment.1,2,3 The SSPC and NACE documents are used by the coatings professionals. In these documents, the distinction is made that blast cleaning or blasting involves the use of solid abrasives whereas water cleaning or water jetting is the use of water alone without abrasives. "Water Blasting" is such a generic and wide-spread term that it hasn't been defined in the consensus process.

Wet Abrasive Blast Cleaning (WAB) covers procedures, equipment, and materials involved in a variety of air/water/abrasive, water/abrasive, and water-pressurized abrasive blast cleaning systems. Air/water/abrasive blasting is the specific cleaning method in which water is injected into the air/abrasive stream generated by conventional air-pressurized abrasive blasting equipment. Water/abrasive blasting is a cleaning method in which abrasive is injected into the water stream generated by conventional fluid pumps. Other generic terms to describe specific air/water/abrasive blast cleaning methods are: Water Shroud or Wet-Head blasting, wet blasting, low volume water abrasive blasting, and slurry blasting. Other generic terms to describe specific water/abrasive blast cleaning methods are: slurry blasting, abrasive water jet (AWJ), or abrasive injected water jetting/blasting (AIWJ).

High Pressure Water Jetting (HP WJ) is cleaning performed at pressures from 70 to 216 MPa (10,000 to 30,000 psi). Ultrahigh Pressure Water Jetting (UHP WJ): cleaning performed at pressures above 216 MPa (,000 psi). Low Pressure Water Cleaning (LP WC) is cleaning performed at pressures less than 34 MPa (5,000 psi) High Pressure Water Cleaning (HP WC) is cleaning performed at pressures from 34 to 70 MPa (5,000 to 10,000 psi).

The terms hydroblasting, hydrojetting, water blasting, and water jetting describe the process in which pressurized water is directed through a nozzle to impact a surface. However, it is noted that the terms hydroblasting or water blasting is used generically to describe cleaning methods that range from low pressure water cleaning to ultrahigh pressure water jetting.

In the coatings industry, water jetting does not provide the primary anchor pattern. The use of water alone is primarily for recoating or relining projects for which there is an adequate, preexisting profile. Abrasive and water combinations can be used on older substrates or new projects to establish a new profile or anchor pattern

3. COATINGS FAILURES AND SURFACE PREPARATION

In the world of corrosion control and painting, it should be obvious to everyone that the job is to get the surface clean enough to accept the paint system. This process is called surface preparation. Surface Preparation is- creating the situation so that the coatings will perform as expected. Remarks in this paper will be limited to processing metal substrates rather than wood, concrete, or plastic and will not include chemical processes such as etching or phosphating.

If you don’t produce a clean surface so that the paint will adhere, the world will move elsewhere. DO a GOOD JOB, the world will beat a path to your door. Expectations for the quality of

surface preparation in coatings have escalated in the past few years. Change increases exponentially. This is the trend of the future. Preparing for change is preparing for the future. Using water in surface preparation, with and without abrasive, is part of the future. Think of the future of your business. If you adapt what you see and hear to your particular needs, you will be part of the future.

It is frequently said that ninety percent (90%) of all coatings failures are the fault of the surface preparation. It is also said that "seventy-five percent (75%) of all coating failures are the fault of the contractor." There are many factors that influence the performance or lifetime of a coating system in addition to the surface preparation, such as formulation, application, and service conditions. Lou Vincent examined failure modes of protective coatings in a presentation to SSPC in November, 1998 and identified twenty-two types.4 Three of those twenty-two failure modes are directly related to surface preparation- adhesion loss, blisters, and delamination. Those three failure modes accounted for 58% of the failures in 55 field case occurrences and 46% of the failures in 101 literature articles occurrences. While this is not the 75-90% generally cited, adhesion loss, blisters, and delamination are clearly the primary failure modes. The other 40-50% of the failures are spread between nineteen different types of failures.

The use of water in maintenance applications, not new steel construction, can have a very positive increase of the adhesion of the coatings and can reduce the chance for blisters and delamination. This positive benefit is why the use of water is the future evolution of surface preparation.

4. THREE ELEMENTS FOR A SUCCESSFUL PROJECT

People are driven to include water by environmental, safety, and economic considerations. They are not embracing water for the benefit of enhanced performance. To make water work in a project, you have to understand that THREE viewpoints must converge in bid specifications and they must all be represented in the negotiations and planning of a project.

The viewpoints of the owner/operator contractor and coatings manufacturer must all come together.

This may seem obvious but it is an often neglected principle. The guarantee for a good job is forced on the coatings manufacturer and contractor. The contractor may be prevented from using wet abrasive blasting (WAB)2 or water jetting (WJ)3 even though the coatings manufacturer and contractor both agree that WAB or WJ may be preferable to clean a surface if the client or owner only has knowledge or training in dry abrasive blast cleaning. Why?- because "the customer (in this case, the owner) is always right." If the customer only has experience in dry abrasive blasting, then the contractor and coating manufacturers working together must overcome steep opposition and provide education.

People in the coatings and maintenance industry are afraid of change. There is a lot of resistance towards change. It is easy to understand. Mistakes come back to haunt us. As an industry, we are to be blamed for slow acceptance-because we don’t talk to each other. Everybody is jealously guarding their secrets. If an engineer learns something that will give him lower maintenance costs or an edge on the competition, he doesn't like to share that secret. The goal of zero defects on every job is a slow, ongoing process. This presentation is part of education. Education is the key to understanding.

5. THREE COMPONENTS OF SURFACE PREPARATION

Surface Preparation- creating the situation so that the coatings will perform as expected.

There are three components to Surface Preparation - All are necessary even though the emphasis in the past has been only on visible cleanliness and anchor profile.

Visible Cleanliness Anchor Profile Invisible Contaminants

Everyone in the coating industry is trained on the visible requirements from day one. The coatings manufacturers control the anchor profile requirements. The third component, Invisible Contaminants, is one component that people are still unaware of even after at least fifteen years of education. All three components are all equally important. While all three are necessary for good coatings performance, it is the last component, the invisible contaminants, that demands water and which requires reform.

The addition of water in surface preparation evolution is occurring because coatings manufacturers have recognized the secret and success of water in dealing with invisible salts. The coatings manufacturers have really understood that water is the "True Grit of the 21st Century." The coatings manufacturers have come forward with videos, pictures, and have rewritten their specifications so that surfaces can be cleaned with dry abrasive blasting and/or various water/abrasive methods.

One major obstacle of the acceptance of water in surface preparation is the appearance. Another major obstacle is the formation of flash rust. Part of the maintenance industry will never accept the appearance of the surface when water is used in surface.

5.1 ANCHOR PROFILE

5.1.1 NEW METAL

First how does one create the profile on a new piece of metal? The profile or anchor pattern is specified by the coating manufacturer. In simplistic terms, the profile of the substrate is generally considered to be the dominant factor in coating adhesion.

Water Jetting by itself is generally not used to create the initial profile even though creating a surface profile can be accomplished with water jetting alone on small objects with careful

controls. 5,6 Automated equipment must be used to control the depth, transverse rate, and stand-off distance. The process is too slow for large pieces. However, when the profile is produced by water alone, the adhesion is greatly enhanced.5

The major surface profile on a metal substrate is defined by the abrasive and is typically formed by a dry, abrasive blast technique. Because of environmental restraints on visible dust, Wet Abrasive Blasting (WAB) is finding a market in new steel construction. WAB covers techniques which range from mostly abrasive, mixed with a little water to suppress the dust, to mostly water with a little abrasive. The pressure range of the water flow can be anywhere from 50 psi to 40,000 psi.

The anchor profile, or pattern, on the substrate is specified by the coatings manufacturer to a depth, such as 0.002-0.003 inches (50-75 microns). Rounded particles such as steel shot give a rounded, crater-like appearance where the width of the depression is greater than the depth. It is thought that hardened sharp angular abrasives tend to cut into the metal, leaving sharp edges, creating hackles (small slivers of steel standing perpendicular to the surface). Particles moving faster will make a deeper indentation compared to the same particle moving slower.

An analogy is throwing a baseball at a mud flat. Throw a large softball relatively slow and you will make a rounded impression with a lip. Throw a small hard ball relatively fast and you will make a deeper rounded impression. Throw a sharpened pyramid at an angle, and you will create a ridge. Some of the mud will splatter off, but most of the mud gets shifted to the new profile.

Abrasives do not necessarily remove the metal because metal is malleable, but you are creating a macroscopic pattern. This pattern may or may not remove existing corrosion cells.7 This initial profile provides the cleaned nib to which the paint adheres.

5.1.2 OLD METAL

There are many situations where abrasives are needed when older surfaces are being blasted. Abrasives are used in tight corners and for the back side of plates where the particles can be rebound or ricochet. In marine areas, there is frequently a very tightly adherent black layer of rust which is resistant to removal by water jetting alone. Addition of a little abrasive into the water stream will speed the production rate and help break this brittle layer. Abrasives can be used to ricochet on all sides of a small compartment whereas it may be difficult to direct a jet stream of water towards all the surfaces.

Abrasives change the existing profile. Abrasives erodes or abrades the surface from the top. A US Standard 100 mesh screen has openings for 125 micron particles. When the contractor is cleaning with 125 micron particles, contaminants which are in cracks or crevices or pits simply cannot be reached or removed. Crevices become filled with spent abrasive when a contractor is trying to remove pack rust between plates. Subsequently the paint gets applied over "clean" abrasive and fails prematurely. If there are invisible contaminants on the surface, abrasive blasting can drive the contaminants into the surface or form a pocket of metal in which the contaminant is buried.

Waterjetting can be described as a series of small droplets in the 5-10 micron range hitting the surface at supersonic speeds. The droplets implode (cavitate) and drill through coatings or rust;

then spread laterally and shear at the interface, much like ultrasonic cleaning, to lift materials. A series of microscopic “pock marks” form on the macro surface. The craters and pits get "deep cleaning."

The measured profile in gross terms, for example 0.002inch (50 microns), is still the same for a surface cleaned by abrasive and by water jetting, but the microscopic details are different. The amount of surface area per square unit area is increased for the WJ cleaned surface. Figure 1 and 2.

Abrasive blasting changes the surface from the top down; water cleans the surface from the bottom of the pits up. These two different types of actions lead to two distinct visual appearances. Waterjetting cleans the existing profile and opens it. Abrasive blasting ignores the pits and cracks. There is a synergistic effect in using abrasives and water because you can get the advantage of both processes.

In a direct comparison of UHP WJ with abrasive blasting, Materials Evaluation Laboratories concluded “The pressurized water method was considered the best preparatory cleaning for non-destructive inspection. It offered a more authentic representation of the surface than the other methods evaluated….Pressured water had minimal disturbance of micro-structural features. ”8

In a direct comparison of water blasting at 10,000 psi versus abrasive blasting for penstock relining,9 Tom Aldinger reported that water blasting would give as good or better adhesion than abrasive blast to SSPC SP10 (near-white) on 60 year-old pen stock. Water blasting produced a clean surface without rust and loose paint residues. Atlas Cell testing in deionized water at 140 Deg. F was then used to compare immersion service performance for coatings on the water blast and abrasive blast surfaces. At the end of the Atlas Cell test, the investigators found a thin film of water and black rust under both the urethane and epoxy coatings on the abrasive blast surface with complete adhesion failure in the immersion zone. The water blast surface had coating adhesion 3 times greater compared to the coating on the abrasive blast surface. Any substrate corrosion on the water blast surface was local without any underfilm spreading. Underfilm corrosion has also been noted in cases where salt was deliberately added to the surface even though the paint was applied before any rust was present.10

“Adhesion begins at the bottom of the pits” said James Denny, Vice-President of International Coatings at Corrosion96. Water Jetting cleans the bottom of the pits. It is the experience of International Coatings and the marine industry that coatings adhere better and last longer on surfaces which have been cleaned by Water Jetting. Coatings manufacturers understand that when you use water for cleaning a profile you get better adhesion sometimes as much as two fold. Van Kuiken's patent illustrates this point. The micro profile is fractal for waterjetting. Loss of adhesion as a failure mode disappears.

5.2 INVISIBLE CONTAMINANTS

Invisible contaminants such as oil and grease generally lead to delamination as a coating failure. Delamination also can be caused by a minimal substrate profile. Invisible contaminants such as salts, chemicals, or water soluble substances lead to osmotic blistering as a coating failure mode. The removal of the invisible contaminants leads to longer performance by the coating system.

The ability to remove chemical contaminants (salts), particularly from badly pitted and corroded steel, is a major advantage of the water jetting process.11,12

WJ and WAB do such a good job of removing invisible contaminants from the surface, even if intact coatings are left on, that blisters from chemical contaminants and delamination from oil and grease disappear.

5.3 VISIBLE APPEARANCE

If WJ and WAB are so good at surface preparation, why is there a resistance for its adoption? Surfaces cleaned by water alone do not look like surfaces modeled by abrasives. Flash rusting on a steel surface can occur very quickly as a result of the very fine, sharp edges. Most of the resistance is based on the visible appearance.

Contractors, inspectors, and coatings personnel use the SSPC/NACE and ISO written standards and visual reference photographs for training and acceptance on jobs. The written standards include:NACE NO. 5- SSPC SP-12 for water jettingSSPC SP-5 for abrasive blastingSSPC SP-10 for abrasive blastingSSPC SP-6 for abrasive blastingSSPC SP-7 for abrasive blasting

Visual reference Photographs include:Dry Methods

ISO 8501-1 for dry abrasive, hand-tool or power-tool cleaning, flame cleaningSSPC VIS-1 for dry abrasive blast cleaningSSPC VIS-3 for hand and power tool cleaning- This shows removal of coatings.

Wet MethodsInternational Paint For Water Jetting issued in 1994International Paint for Slurry Blasting (Wet Abrasive Blast cleaning) Hempel's Photo Reference for Steel Surfaces cleaned by Water JettingJotun Photo Reference for examples of flash rustingSchiffbautechnisch Gesellschaft No. 2222 Guide for water jettingSSPC- VIS 4 (I) NACE No. 7 Interim Guide and Visual Reference Photographs for Steel Cleaned by Water Jetting- issued in 1998

Even though the visible references are for supplemental purposes in the US, in practicality, people use them as a primary standard. SSPC VIS-1 and ISO 8501-1 are the two visual reference photographs series used in training. They depict dry abrasive cleaned steel which have not been painted. Emphasis is on uniformity. Inspectors and owners are just beginning to use the VIS-4 (I) Reference Photographs for Water Jetting ( which is the same set of photos as International Paint Water Jetting Standards. These also only depict unpainted steel.

As we go through the standards, keep in mind that visual reference photographs are designed to be illustrative of the situation. Direct correlation to existing dry media blasting standards is inaccurate or inappropriate when describing the capabilities of waterjetting and the result achieved with waterjetting as a process.

Abrasives hit from the top, erode the surface, provide plastic flow to the metals, tend to make the surface look uniform and “erase” different areas. There is a tendency to drive existing contaminants into the surface. Observers with an experienced eye tend to neglect the pits. They tend to look at the top surface.

WJ stresses the adhesion between two materials. WJ retains the metallic surface profile, tends to clean the pits first and leave material at the top peaks, and accentuate the non-uniformity of a surface. The experienced observer sees black stains on the top where heavy rust was present, or coatings on the top of the surface- rather than stains in the bottom of the pits so the observer see something which is a new experience even though the pits are cleaned.

The visual photographs SSPC VIS-1 and ISO 8501 only depict the situations of rusted steel. Water jetting is used primarily in removal of coatings, where frequently the objective is to retain as much tightly adherent coating as possible. There was a need to address the question of maintenance in visual reference photographs.

The following phrase exists in all the written standards. “Acceptable variations in appearance that do not affect surface cleanliness include variations caused by type of steel, original surface condition, thickness of the steel, weld metal, mill or fabrication marks, heat treating, heat affected zones, blasting abrasive, and difference in the blast pattern.” Figures 3 and 4 illustrate WJ-1 cleaning and the variation in appearance. That variation does not appear in the abrasive photographs.

5.3.1 CLEAN TO BARE SUBSTRATE- "WHITE METAL"

NACE No. 5- SSPC - SP 12 WJ-1WJ-1 surface shall be free of all previously existing visible rust, coatings, mill scale, and foreign matter and have a matte metal finish.

ISO 8501-1 Sa 3When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and shall be free from mill scale, rust, paint coatings and foreign matter. It shall have a uniform metallic color.

SSPC-SP 5 NACE 1When viewed without magnification, the surface shall be free of all visible oil, grease, dust, dirt, mill scale, rust, paint, oxides, corrosion products, and other foreign matter.

5.3.2 VERY THOROUGH CLEANING, "CLEAN ALMOST TO BARE SUBSTRATE"

NACE No. 5- SSPC SP-12 WJ-2WJ-2 surface shall be cleaned to a matte finish with at least 95 percent of the surface area free of all previously existing visible residues and the remaining 5 percent containing only randomly dispersed stains of rust, coatings, and foreign matter.

SSPC SP 10 NACE No. 2 “Near White Blast Cleaned Surface”

RANDOM staining shall be limited to no more than 5 percent of each unit area of surface ... , and may consist of light shadows, slight streaks, or minor discoloration caused by stains of rust, stains of mill scale, or stains of previously applied paint.

ISO 8501-1 Sa 2 1/2 Very Thorough Blast Cleaning:When viewed without magnification, the surface shall be free from visible oil, grease and dirt, and from mill scale, rust, paint coatings and foreign matter. Any remaining traces of contamination shall show only as slight stains in the form of spots or stripes.

HB 2.5 Very Thorough Hydroblast Cleaning (International Paint)When viewed without magnification, the surface shall be free from visible oil, grease, dirt, loose rust, paint coatings and foreign matter. A brown-black discoloration of ferric oxide may remain as a lightly adherent thin film on corroded and pitted steel.

In conversations with major coatings manufacturers, Dr. Frenzel has come to understand that the coating manufacturers' technical staff are not including the brown-black discoloration of ferric oxide as part of the staining criteria. They are looking for stains of material other than black ferric oxide. Thus a WJ-1 or WJ-2 may be extremely mottled if the steel surface has been heavily corroded.

5.3.3 THOROUGH CLEANING, “COMMERCIAL BLAST”

NACE No. 5- SSPC SP-12 WJ-3WJ-3 surface shall be cleaned to a matte finish with at least two-thirds of the surface free of all visible residues (except mill scale), and the remaining one-third containing only randomly dispersed staining of previously existing rust, coatings, and foreign matter.

Notice that we are now including the idea that mill scale might remain on the surface. This is recognition of the types of projects in which WJ is used. The language is for staining, not for the coating itself. However, the marine industry is interpreting this to mean the coatings and foreign matter can remain on if it is dispersed.

SSPC SP- 6, NACE No. 3 Commercial BlastRandom staining shall be limited to no more than 33 percent of each unit area of surface as defined, and may consist of light shadows, slight streaks, or minor discoloration caused by stains of rust, stains of mill scale, or stains of previously applied paint.

ISO 8501 Sa 2 Thorough Blast- CleaningWhen viewed without magnification, the surface shall be free from visible oil, grease and dirt, and from most of the mill scale, rust, paint coatings and foreign matter. Any residual contamination shall be firmly adhering.

HB 2 Thorough Hydroblast Cleaning (International Paint)When viewed without magnification, the surface shall be free from visible oil, grease, dirt and from most of the rust, paint coatings and foreign matter. Any remaining contamination and staining shall be firmly adherent.

Tightly adherent coatings, mill scale and rust can remain in the ISO definition, but not in the SSPC/NACE definitions.

5.3.4 BRUSH OFF BLAST, REMOVAL OF LOOSE MATERIAL

NACE No. 5/ SSPC SP-12 WJ - 4WJ-4 surface shall have all loose rust, loose mill scale, and loose coatings uniformly removed.

SSPC SP- 7 Brush Off BlastTightly adherent mill scale, rust, and paint may remain on the surface. Mill scale, rust, and paint are considered tightly adherent if they cannot be removed by lifting with a dull putty knife.

ISO 8501 Sa 1 Light Blast CleaningWhen viewed without magnification, the surface shall be free from visible oil, grease, and dirt, and from poorly adhering mill scale, rust, paint coatings and foreign matter.

GLOBAL PERSPECTIVE

For WJ-1 "Clean to bare substrate" and WJ-2 "very thorough cleaning" specifications, the WAB and WJ appearance is dark compared to dry blasting. It may also be streaked from the drying of the water. This appearance is very normal and accepted by the coatings manufacturers. On older steel, heat marks, tooling, and dark stains in corrosion areas remain very visible with WJ. WJ accentuates those differences; abrasive blasting tends to make the surface "appear" uniform.

When VIS-4(I) was issued, the NACE/SSPC task group modified the language to accommodate both the adherent (ISO) and the percentage (NACE-SSPC) concepts and started to bring the European and United States philosophies closer together. Because of obstacles arising in the field in refurbishment projects, there was an immediate need for photographs depicting coatings removal. In January, 1997, after a review and selection of new photographs, the National Shipbuilding Research Program SP-3 Technical Advisory Chairman for Water Jetting Photographs requested an early revision of NACE No.5- SSPC SP-12 so that the language might reflect the retention of coatings. It was obvious from the selection of the photographs and the issuance of the Hempel's reference set that there was a wide gap between the language and the practice. In all of these cases, technical representatives of coatings manufacturers, owners, and experienced WJ contractors were involved.

The perception of percentage coverage is an unrecognized problem. Every experienced inspector thinks that he can tell what 5% and 33% coverage is. That simply is not true. This was very evident as the new photos were being screened.

Coverage is a topic to itself and is depicted in illustrations of 5% and 30% coverage from "The Book of Spots."13 Each person views a surface differently. Whether the spots are sharp or diffuse, nearly the same color or contrasting colors, on a uniform, lightly profiled or a non-uniform, heavy pitted surface, will make a difference. Since 1996, Dr. Frenzel has been educating the experienced personnel first on the NSRP Technical Advisory Committee and subsequently the NACE/SSPC task group on percentage coverage. Figures 5, 6, and 7 illustrate three different representations of five percentage coverage.

In practice, the marine coatings industry embraced NACE No. 5/ SSPS SP-12 and immediately interpreted it to allow islands of tightly adherent paint to remain as compared to stains of paint because it is used in maintenance and repainting. The original "staining" language arose because solid particles don't get into the crevices. The paint remains as stains in the pits and crevices. In WJ without abrasive, intact coating remains on the top of the surface. The new photos under consideration where coatings are being removed all depict the retention of coatings. Coatings manufacturers have positively endorsed this position.

With the advent of computer digitization, new photos are also being considered for SSPC- VIS 2/ASTM D 610 "Standard Method of Evaluating Degree of Rusting On painted Steel Surfaces." The concept of percentages with large, medium, and small, pinpoint spots is a challenge because the appearance in pin point corrosion at 30% is that the entire surface is covered.

6. SUMMARY

The written definitions are similar in that they describe four visual cleanliness conditions. They differ with respect to the presence of mill scale and tightly adherent coating as compared to percentage staining. Based on the discussion of the task group members, it is the author's opinion that the current ISO photographs and the SSPC/NACE written definitions are inadequate to address the problems of retention of sound coatings in maintenance. The appearance of old metal surfaces cleaned by WJ without any abrasive is very different from those cleaned with abrasives.

There is no discrepancy when all coatings and rust layers are removed by WJ or WAB. However, WJ finds its forte in partial removal of coatings. It is the partial removal and spot blasting with WJ and WAB with soft abrasives that is forcing the adoption of new visual photographs and a revision of the written standards language. The WJ task groups of NACE, SSPC, and ISO are addressing this question. Water jet cleaning is bringing the European and United States standards organizations together into a coalition effort.

7. ACKNOWLEDGEMENTS

Thanks to International Paint, Jotun, Hempel's, Cavi-Tech Inc. for permission to use their photographs in non-commercial presentations. The members of the SSPC and NACE task groups have volunteered thousands of hours. Special thanks to Aqua-Dyne, Butterworth Jetting, Carolina Equipment & Supply, Flow Int., and NLB Corporation, Doug & June Koppang, Aulson Co., Cavi-Tech, Fluidyne, Freemyer Co., Hartman-Walsh Painting, UHP Projects, Valley Systems,, Leo Kosowan, Roland Hernandez, and Dan Bernard for support and discussion.

1 “Recommended Practices for the Use of Manually Operated High Pressure Water Jetting Equipment,” WJTA, St. Louis MO

2

? SSPC-TR2/ NACE 6G198, SSPC/NACE Joint Technical Report, "Wet Abrasive Blast Cleaning," issued May, 1998. SSPC Tel: 412-281-2331

3 Joint Surface Preparation Standard NACE No. 5/SSPC-SP 12; "Surface Preparation and Cleaning of Steel and Other Hard Materials by High- and Ultrahigh-Pressure Water Jetting Prior to Recoating,", issued 1995. NACE Tel: 281-228-6200 Separate document "Surface Preparation of Concrete" includes WJ cleaning of concrete.

4 Vincent, L.D. , "Increasing the Value of Coatings", Proceedings of the SSPC 1998 Seminars, November, 1998, SSPC 98-11 "Failure Modes of Protective Coatings and Their Effect on Management," p. 125-128.

5 VanKuiken, Jr., L.L., Byrnes, L.E., & Kramer, M.S., High Pressure Water Jet Method of Blasting Low Density Metallic Surfaces, U.S. Patent 5,380,564, Issued Jan. 10, 1995

6 Taylor, Thomas A., "Surface Roughening of Metallic Substrates by High Pressure Waterjet," Surface & Coatings Technology, Vol. 76-77 ( 1995), 95-100

7 Frenzel, Lydia M.; Nixon Jonell, "Surface Preparation using High Pressure Water Blasting," NACE Corrosion89, paper No. 397, April, 1989

8 Materials Evaluation Laboratories, Claude Mount, January 1991, work performed for Shell Oil Company, Report number 9501

9 Aldinger, Tom (Bechtel), Viswanath, Bala (Pacific Gas and Electric), Dick Vass (Vass Industries), SSPC 1994 Conference, Industrial Maintenance Coatings- Current Trends and Practices, “Water Blasting versus Abrasive Blasting for In situ Penstock Relining”

10 Morcillo, M. & Simancas, J., JPCL, Sept. 1997, p. 40 “effects of Soluble Salts on Coating Life in Atmospheric Service" and G.C. Soltz., “The Effect of Substrate Contaminants on the Life of Epoxy Coatings Submerged in Sea Water,” National Shipbuilding Research Program, March, 1991, task 3-89-2

Figure 1. Steel Cleaned with HP WJ130x magnification. Upper right white bar is 10 microns. originally blasted, then rusted, then cleaned with HP WJ to “white metal” WJ-1. You can see the original impacts of the abrasive. All crevices are cleaned; the dark areas are shadows.

Figure 2 Steel Cleaned with Abrasive130x magnification. Upper right white bar is 10 microns. Originally blasted, then rusted, then blasted to white metal. You can see the impacts, the flattened surface. The dark areas are materials caught in the lower layer under the top surface.

Figure 3 Multilayer Paint cleaned with WJOriginal size 6 x 10 inchespartial removal of paint. Complete removal on lower edge.

Figure 4 WJ-1 "Clean to bare substrate"Upper right and left show typical examples of carbon stain and the appearance of corroded steel which is cleaned to WJ-1. The steel under the paint is uniform and appears "white" in this black and white printing.

11 SSPC-VIS 4(I) NACE No. 7 "Interim Guide and Visual Reference Photographs for Steel Cleaned by Water Jetting, SSPC Pub. 98-07; NACE Item NO. 22016

12 Howlett, Jr., J.J. and Dupuy, R., Ultrahigh-Pressure Water Jetting for Deposit Removal and Surface Preparation, Materials Performance (MP), No.1, Jan, 1993, p. 38

13 Advisory Council, "The Book of Spots", depicting 1-30% coverage and 20% with different relative spot sizes. Computer generated to be exact.

Figure 6 Five percentage coverage-Smaller spots in a distribution of 1:10

Figure 7 Five percent coverage-Uniform distribution of Very Small Dots.Figure 5 Five Percentage coverage-Larger Spots in a Distribution of 1:10